Manufacturing method for a plastic element

ABSTRACT

The present invention relates to a method and a mould for manufacturing plastic element as well as a plastic element having oppositely arranged eye parts where oppositely one eye part in relation to a substantially centrally placed stem is arranged a recess on the opposite side, where the manufactured plastic elements for example are chain links or a conveyor belt, and where the mould comprises two mould halves, where each part comprises protruding core parts and further a plastic element manufactured by the mentioned method of manufacture in the mentioned mould, where in the eye parts are provided through-going openings in the chain links with respect to the travel direction.  
     It is the object of the invention to simplify moulds and the molding process as well as reduce the requirements for the size of the molding machine.  
     This is achieved by a method where the mould comprises two halves with offset and side placed core parts, which create recesses between side placed eye parts on one side and cavities on the oppositely arranged eye parts, where the ultimate ends of the core parts on one mould half is brought into contact with side places interior parts of the core parts on the other mould part by closing the two-part mould. In this manner, pin bolts which until now have shaped the openings in the third dimension become superfluous.

TECHNICAL FIELD OF THE INVENTION

[0001] The present invention relates to a method as well as a mouldsystem for the manufacturing of plastic elements as well as a plasticelement, said element having oppositely offset eye parts, whereoppositely one eye part on one side of a stem is arranged a recess onthe opposite side, where the manufactured plastic elements for exampleare chain links for conveyor belts and where the mould system comprisestwo mould halves such that each mould half comprises extending coreparts, where the core parts are made with a taper and further that eachplastic element manufactured by the method and by the mentioned mouldsystem is a chain link, which is suitable for being assembled with othercorresponding or identical chain links in order to create a flexibleconveyor belt, where the element comprises a stem on both sides of whicheye parts are arranged such that directly opposite an eye part on oneside of the stem is arranged a corresponding recess on the opposite sidesuch that two identical elements can be brought together and in thismanner comprise overlapping eye parts such that a through-going apertureis provided in the chain link's transverse width direction.

BACKGROUND OF THE INVENTION

[0002] Chain links are among other things used for constructingconveyors, which conveyors are relatively stiff in one dimension,usually the width, whereas they are very flexible in the transportdirection. Furthermore, it can be achieved that the conveyor is veryflexible for deflections in the conveyor's transport plane.

[0003] Conveyors as well as chain links as described above are knownfrom for example U.S. Pat. No. 6,216,854. The known conveyors areconstructed by assembling a number of chain links which are mutuallyconnected, where each chain link consists of a stem oriented in atransverse direction to the transport direction of the conveyor, andprotruding from the stem in the plane of the conveyor eye parts arearranged. In every eye part perpendicular to the transport direction,approximately in the middle of the chain links' thickness, is arranged athrough-going aperture. Furthermore, the protruding eye parts on bothsides of the stem are arranged in a offset manner, such that on one sideof the stem an eye part is formed and directly opposite the eye part onthe other side of the stem a recess is provided. By means of thisconstruction two chain links can be assembled such that the eye parts onone side of the stem fit into the recesses of an adjacent chain link.When assembling the chain links in this manner, the apertures formed inthe eye parts in the thickness dimension will overlap such that oneaperture is formed through the two assembled chain links transverse tothe conveyor's transport direction. In order to assemble the chain linksinto a conveyor belt, an assembly pin is inserted into the overlappingapertures. If the aperture has an oval shape, it is possible for eachseparate chain link to move relatively to the adjacent chain links andat the same time stay connected to said chain links by means of theinserted assembly pins. Typically, the pin is a steel axle.

[0004] Due to this possibility of relative displacement between twoadjacent chains links, it becomes possible for the conveyor to beside-flexible in a direction parallel to the plane of the conveyor.Furthermore, as each chain link can rotate around the inserted assemblypin, the conveyor obtains a large degree of flexibility in a planeperpendicular to the conveyor's traveling direction.

[0005] The manufacture of this type of plastic element is usuallycarried out by a plastic molding process, for example injecting molding,where the element is cast in a lying position. By lying is in thisconnection to be understood that the mould is shaped such that when thetwo halves of the mould are closed and forced together, each separatechain link is cast such that the transport plane of the chain link, i.e.the plane where an assembly of elements constitute a conveyor belt, isperpendicular to the closing direction of the mould. After closure ofthe two mould halves, but prior to injection, a number of pin bolts areinserted into the mould corresponding to the number of apertures whichneed to be formed in each chain link in order to provide the aperturesin the thickness dimension for the later assembly of the chain linksinto a conveyor as discussed above.

[0006] After insertion of the pin bolts into the plastic mass, the massis introduced into the mould under high pressure, just as the two mouldhalves are forced together with a very high pressure, typically fromabout fifty to hundreds of tones. With this pressure a number of chainelements can be formed in each mould. This means that more elements aremanufactured in one molding cycle. After the plastic mass has beenforced into the mould, the pin bolts are withdrawn. Next the two mouldhalves are moved apart and the finished plastic elements are therebyreleased.

[0007] The dimension of moulds for this type of element is relativelylarge as the mould consists of the width of the elements plus the lengthof the pin bolts, which usually corresponds to the width of theelements, since one pin bolt has to create openings throughout the eyeparts in the entire width of an element in the thickness dimension inorder to be able to assemble the chain links into a conveyor belt asdiscussed above. Furthermore, in the end of the pin bolts it isnecessary to arrange hydraulic cylinders which can insert the pin boltsand withdraw the pin bolts again after the plastic mass has beenintroduced into the mould. Hereby the space requirements for the mouldis substantially larger than the size of the element. Furthermore, it isnecessary to provided a large force in order to force the two mouldparts together, since the surface area of the elements in the mould'sclosing surfaces multiplied by the pressure in the plastic mass duringthe casting process result in a large pressure, which influences themould halves with a relatively large resulting surface due to theorientation of the elements in the mould.

[0008] A similar casting process as discussed above with reference tothe background art document U.S. Pat. No. 6,216,854 is disclosed in WO9738925. This conveyor is especially produced for providing good coolingto products placed on the conveyor. Therefore, the surface of theconveyor is perforated with rather large perforations such that the aireasily can flow through the surface of the conveyor. During the moldingprocess, which is carried out according to the principles describedabove with respect to U.S. Pat. No. 6,216,854, the two mould halves arebrought into contact in order to provide the large recesses in thesurface of the chain links. The apertures for inserting assembly pins asdescribed above are manufactured in exactly the same way as the chainlinks disclosed in U.S. Pat. No. 6,216,854 and further the element isarranged in the mould, i.e. lying, as disclosed above.

SUMMARY OF THE INVENTION

[0009] One object of the present invention is to improve and simplifythe moulds for the casting process and the same time reduce therequirements to the size of the injection mould machine.

[0010] This is achieved according to the present invention with a methodwhich is particular in that

[0011] the mould for the molding process comprises two halves withprotrusions/core parts which are moved into a position where theprotrusions/core parts are arranged in a side-by-side manner prior toinjecting the molding material;

[0012] that the protrusions/core parts on one mould half create therecesses between neighboring eye parts on one side and the cavity insidethe oppositely arranged eye parts on the other side of the stem;

[0013] that the ultimate ends of the protrusions/core parts on a firstmould half during closing/injection are brought into contact with theside-by-side arranged interior ends of the protrusions/core parts on theother mould part, and

[0014] that the mould halves after injection of mould material arewithdrawn, whereby a through-going aperture through the eye parts in thechain links width direction is created.

[0015] In the description of the moulds above, ultimate end and interiorend of the protrusions/core parts shall be understood such that thecores protrude from the mould base. The mould base is adjacent theinterior part within the terminology used in this application and theultimate end of the core is therefore the pinnacle of the protrudingprotrusion/core part, i.e. the part of the protrusion/core part furthestfrom the base.

[0016] Further, where reference is made to the traveling direction ofthe conveyor. This is understood as the direction in which the conveyorwill transport goods placed on said conveyor.

[0017] The chain links have a top side on which the goods to betransported on the conveyor will be placed. The bottom side is oppositethe top side. In relation to the transport direction of the conveyor orthe direction perpendicular to the traveling direction is the width ofthe conveyor or chain link respectively.

[0018] By designing the moulds such that the cores for the eye parts ina first mould half are offset in relation to the second mould half,where the cores have corresponding side surfaces which during thecasting process are in abutment such that the mould in its closedcondition has contact points between the two mould halves. The pin boltswhich in the prior art created the apertures in the third dimensionbecome superfluous. This results in a number of advantages. As the pinbolts neither need to be inserted nor drawn back, a molding cycle can becompleted faster and consequently there is a substantial saving in timeby being able to cast the elements directly without the intermediateprocess of inserting, respectively removing, the pin bolts andfurthermore the injection molding machine can be manufactured cheaper inthat the mould is substantially smaller and therefore does not require alarge injection molding machine.

[0019] As discussed above traditional moulds have a size correspondingto the width of the elements plus the length of the pin bolts plus thehydraulic cylinders necessary in order to be able to insert and withdrawpin bolts in order to create the apertures in the third dimension.According to the method of the present invention the pin bolts as wellas the hydraulic cylinders can be excluded such that the entire mouldsize substantially corresponds to the width of the elements. Hereby itbecomes possible to utilize substantially smaller injection moldingmachines which in turn results in substantially lower production costs.Furthermore, the mould themselves become cheaper to manufacture in thatthey are smaller.

[0020] Yet another advantage achieved by being able to not use pin boltsin order to create the apertures in the third dimension is achieved inthat pin bolts used in traditional moulds for forming of the aperturesbecome worn. During the injection molding process and during thehardening under high pressure the plastic has a tendency to creep up to2%. This creep will cause the plastic to adhere to the pin bolts and dueto the withdrawal of the pin bolts this will cause wear on the pinbolts. This friction wear on the pin bolts means that the apertures inthe elements will have a varying size during the production processwhereby the tolerances between separate chain links will vary which canhave substantial influence on the life expectancy of the finishedconveyor belt. Furthermore, the wear on the pin bolts can result in thatthe apertures in each element can vary and possibly induce castingerrors in the eye parts of the elements which can also influence thefunction of the conveyor belt in a negative direction.

[0021] In a preferred embodiment of the invention the plastic elementsare arranged in the mould such that the elements are placed standing upduring the injection molding process in relation to the closingdirection of the mould. Within the scope of the present invention,standing up shall be understood as the plane wherein the elements in theuse condition, i.e. if chain links as discussed above are beingproduced, will be assembled (the transport plane) in order to constitutean conveyor. Standing up will therefore be the transport plane of thefinished conveyor. This plane is perpendicular to the thickness plane aswell as the width plane of the elements. By the width of an element isunderstood the width of a conveyor belt assembled from chain links.

[0022] Furthermore, by producing the elements where these are standingup during the injecting molding process the closing pressure on themoulds can be substantially reduced in that the surface (thethickness/width of the element which creates the counter pressure on themould halves) can be substantially reduced in comparison to thetraditional method, where the length/width of the elements willdetermine the closing pressure of the mould.

[0023] A plastic element according to the invention is substantiallydifferent from the known type of chain link in that the stem ispenetrated approximately in the middle of the thickness direction, sothat from a recess on one side of the stem an opening through the steminto the oppositely positioned eye part is created. The stem with thebreakthroughs still have the necessary strength, but a substantialsavings on materials is achieved in that the stem in the thicknessdirection of a plastic element according to the invention is comparableto a lattice structure. This lattice structure comprises the plasticelements' outer surfaces and interior connection members which arearranged between the outer surfaces of the plastic element and is placedbetween recesses and oppositely arranged eye parts. The said connectionmembers constitute the limits of the through-going apertures in the eyeparts towards the stem part.

[0024] From WO 97/38925 is disclosed a chain link, a conveyor chain anda method for producing said chain links. In the method for manufacturingthe chain links, the chain links are in the lying down position and themould parts are brought together in order to create the large aperturesperpendicular to the conveyor belt's traveling direction. Theseapertures are provided in order to be able to have a large flow of airthrough the conveyor belt in order to cool objects placed on theconveyor belt. For producing the apertures in the eye parts, traditionalpin bolts are used with the inherent problems as discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] A more complete appreciation of the invention and many of theintended advantages thereof will be readily obtained as the same becomesbetter understood by reference to the following detailed descriptionwhen considering the connection with the accompanying drawings, wherein:

[0026]FIG. 1 is a perspective view of a conventional chain link;

[0027]FIG. 2 illustrates a perspective view of a chain link according tothe invention.

DESCRIPTION OF EMBODIMENTS

[0028] Referring to the drawings, wherein like reference numeralsdesignate identical or corresponding parts throughout and in particularin FIG. 1, there is shown a chain link produced according to thetraditional method. The element 1 has a stem 2 from which eye parts 3protrude in the traveling direction of the conveyor belt. Due todifferent requirements recesses 4 can be arranged in the eye parts 3perpendicular to the surface which constitutes the conveyor belt. Inorder to be able to assemble more chain links into a conveyor belt,apertures 5,6 are arranged in the thickness dimension of the chain linkperpendicular to the transport direction of the conveyor belt andapproximately in the middle of each chain link's thickness dimensionthrough respectively the protruding eye parts on one side on the stemand on the other side of the stem. In the illustrated example theaperture 5 on one side of the stem is in the shape of a circular hole,while the apertures 6 on the other side of the stem are in the shape ofelongated holes.

[0029] When assembling two identical chain links 1 the eye parts withround holes are inserted in-between the eye parts with elongatedapertures. In this manner an overlap between the round holes 5 and theoval aperture 6 is achieved. Through the overlapping apertures a roundaxle is inserted, said axle having an outer dimension substantiallycorresponding to the diameter of the holes 5. Due to the shape of theelongated holes 6 the chain links will be able to move relatively toeach other in the conveyor belt's transport direction. Furthermore, thechain link may be sideways flexible in the plane of the conveyor belt.

[0030] In FIG. 2 is illustrated the corresponding element as illustratedwith respect to the description of FIG. 1, but manufactured according tothe method disclosed in the present invention. Like reference numbers isa factor 10 larger than in FIG. 1.

[0031] In the illustrated example recesses are created in the eye parts30 perpendicular to the plane of the conveyor belt. From the stem 20project eye parts 30 offset arranged such that on one side of the stem20 is arranged an eye part 30 and directly on the opposite side of thestem a recess 70 is provided. As explained above with reference to FIG.1 a number of elements 10 can be assembled to a conveyor belt byinserting the eye part 30 into the recess 70 and thereafter insert anaxle through the overlapping openings 50,60. In this manner a flexibleconveyor belt can be constructed exactly as explained above withreference to FIG. 1.

[0032] The mould according to the invention for manufacturing of theelements, for example as illustrated with reference to FIG. 2, will haveengaging surfaces between the two mould halves corresponding to theopenings 50,60. Where the mould closing direction for an elementproduced as described with reference to FIG. 1 is illustrated by thearrow 8, the corresponding closing direction with respect to the newinventive method according to the invention is illustrated with thearrow 80.

[0033] As is evident from FIG. 2 the surface which created the counterpressure when closing the two mould halves will be substantially less inthat it will only be the width of the eye parts multiplied by thethickness of the element which will create the counter pressure againstthe mould halves, whereas with the manufacturing process for an elementas illustrated in FIG. 1 it will be the entire surface of all the eyeparts 3 as well as the stem 2 which will create the counter pressureagainst the mould halves.

[0034] Contrary to the process known from the above mentioned documentWO 97/38925 it is possible with the manufacturing process according tothe present invention to manufacture chain links which have a solidsurface and still benefit from the manufacturing process as describedabove. The chain links known from WO 97/38925 will inherently, as aresult of the process disclosed in the document, be provided withapertures in order to provide the cooling necessary for that process.

[0035] Above the invention has been described with respect to chainlinks, which chain links by assembling a number of corresponding oridentical chain links can be made into the shape of a flexible conveyorbelt. It should, however, be understood that the invention is notlimited to chain links of the type mentioned above, but the method formanufacturing of plastic elements according to the invention can beutilized in other plastic element producing processes, where recesses inthree dimensions are needed and which are to be manufactured in a greatnumber.

[0036] The method according to the invention is especially developedwith respect to plastic molding processes such as injection molding ofplastic, but can also be used in other plastic forming processes wheremoulds comprising two parts are used.

[0037] Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is,therefore, to be understood that within the scope of the appendingclaims the inventions may be practiced otherwise as specifcallydescribed herein.

What is claimed as new and to be desired by Letters Patent of the UnitedStates is:
 1. Method for manufacturing of plastic elements havingoppositely arranged offset eye parts, wherein there oppositely to an eyepart on one side of a stem is arranged a recess on the opposite side;where the manufactured plastic elements for example are chain links fora conveyor belt and where the method comprises; that the mould for themolding process comprises two halves with protrusions/core parts whichare moved into a position where the protrusions/core parts are arrangedin a side-by-side manner prior to injecting the molding material; thatthe protrusions/core parts on one mould half create the recesses betweenneighboring eye parts on one side and the cavity inside the oppositelyarranged eye parts on the other side of the stem; that the ultimate endsof the protrusions/core parts on a first mould half duringclosing/injection are brought into contact with the side-by-sidearranged interior ends of the protrusions/core parts on the other mouldpart, and that the mould halves after injection of mould material arewithdrawn, whereby a through-going aperture through the eye parts in thechain links' width direction is created.
 2. Method for manufacturing ofplastic elements by plastic molding according to claim 1, wherein themould halves are shaped such that the elements are molded having theclosing direction of the mould halves parallel to the elements'longitudinal direction/conveyor belt's transport direction.
 3. Mould formanufacturing elements in a plastic molding machine according to claim 1and/or 2, wherein the mould comprises two mould halves, where each halfcomprises protruding mould parts, where the mould parts have a taper andwherein the core parts in a first mould half are offset in relation tothe other mould part such that the core parts have correspondingultimate side ends which during molding are in engagement.
 4. Mould formanufacturing elements in a plastic molding machine according to claim3, wherein the ultimate side edges on the protrusions/core parts on afirst mould half in the mould's closed position correspond to offsetinterior side surfaces on the protrusions/core parts on the other mouldhalf.
 5. Element manufactured by a plastic molding process in a two-partmould according to any of claims 1-4, where the element is a chain link,which chain link can be assembled with other corresponding or identicalchain links and thereby create a flexible conveyor belt, where the chainlink comprises a stem on both sides of which perpendicular to thetransport direction of the chain link eye parts are provided such thatdirectly opposite an eye part on the other side of the stem is arrangeda corresponding recess such that two identical chain links can be pushedtogether and thereby have overlapping eye parts and where in the eyeparts are arranged through-going apertures in the chain links withdirection, wherein the stem is broken through such that from a recess onone side of the stem is created an opening into the oppositely arrangedeye part on the other side of the stem.